Simplified pushbutton array with electrical interlock



J. D. BAGLEY April 20, 1965 SIMPLIFIED PUHBUTTON ARRAY WITH ELECTRICAL INTEBLOCK Filed Dec. 26, 1961 FIG.1

CENTRAL PROCESSING CENTER Wm"- III TRANSMITTER 15 FIG.2 Mi

INVENTOR JOHN D. BAGLEY 641 ATTORNEY .ing devices to encode information.

United States Patent 3,179,807 SIMPLIFIED PUSHBUTTON AY WITH ELECTRICAL INTERLOCK John D. Bagley, Ann Arbor, Mich, assignor to International Business Machines Corporation, New York,

N.Y., a corporation of New York Filed Dec. 26, 1961, Ser. No. 162,013 13 Claims. (Cl. 250-208) This invention relates to data processing systems and, more particularly, to terminal data sets employed in such systems for encoding information for transmission from a peripheral stage to a common processing center.

In data systems, for example, of the inventory type, terminal data sets are provided at each of a number of peripheral stages for encoding information for trans mission to a common processing center. These terminal data sets generally include keyboard arrangements which, upon key depression, enter representative information along a communication path to the central processing center. Heretofore, terminal data sets of the prior art have employed mechanical linkage arrangements responsive to key depression for actuating mechanical switch- Certain limitations and disadvantages, however, are inherent in such arrangements. For example, a primary limitation is that the required alignment of mechanical linkages necessarily restricts the number of key arrangements possible for each independent field of the terminal data set and,

accordingly, limits operator efiiciency. Further, the cost of manufacture and assembly and also maintenance of these mechanical linkage is excessive. It has long been appreciated that mechanical linkages are not ideal construction for terminal data sets; however, the utilization of mechanical linkage arrangements has been continued as no other practical constructions of terminal data sets has been heretofore available. While it is true that alternate arrangements have been considered, e.g. electronic, the cost of development and manufacture of such alternate arrangements is objectionably expensive.

Accordingly, one object of this invention is to provide such an alternate arrangement for terminal data sets which is relatively inexpensive to manufacture and maintain and yet reliable in operation.

' Another object of this invention is to provide a terminal data set employing no mechanical linkages.

Another object of this invention is to provide a terminal data set wherein the component arrangements may be modularly packaged to facilitate and also reduce the costs of manufacture and maintenance of such data set.

Another object of this invention is to provide a terminal data set wherein the key arrangement of each field of the terminal data set need not be mechanically aligned but, rather, may be positioned to provide maximum operator efficiency.

These and. numerousother objects and advantages of this invention are achieved and full versatility imparted to a terminal data set by employing opto-electronic arrangements adapted for latching operation in lieu of the mechanical linkages and switches heretofore employed. In accordance with one aspect of this invention, optoelectronic arrangements comprising a number of photoconductive elements adapted to be illuminated by a single light source or neon bulb areassociated one with each key in a field of the terminal data set. One of the photoconductive elements latches the light source when fired on depression of its associated key. While the light source is latched, another photoconductive element provides a visual indicationto the operator; the remaining photoconductive elements serve to encode and, in effect,

store a multibit signal indicative of the associated key until a complete messageis assembled on subsequent depressions of keys in other fields of the terminal data set. The completed message can then be transmitted to the central processing center in accordance with a particular format wherein the multibit signals as well as their respective positions in the message have significance. Accordingly, the time consuming task of message assembly is avoided and fewer characters must be sent to transmit the same amount of information so as to achieve a substantial savings in both transmission and processing costs.

Moreover, the opto-electronic arrangements associated with each field of the terminal data set are interlocked to insure that only one of the opto-electronic arrangements is ina latched condition at any one time. In accordance with another aspect of this invention, the opto-electronic arrangements are multiplied along a common operating voltage bus. While one of the optoelectronic arrangements is in a latched condition, the voltage level along the bus is sufficient to maintain the one opto-electronic arrangement but is insufiicient to develop firing potentials for light sources in any of the remaining opto-electronic arrangements. However, the depression of a key associated with another of the optoelectronic arrangements is eifective to temporarily bias the corresponding light source in excess of its firing potential. A temporary biasing of the selected light source at this time is achieved in accordance with another aspect of this invention by providing an optical switch in the form of a normally illuminated photoconductive element in shunt relationship with a secondary voltage source connected to the far side of the light source. When the key is depressed, the optical switch reverts to a dark resistance state such that the secondary voltage source is coactive with the common operating voltage to bias the selected light source in excess of its firing potential. When the selected light source has fired and while the keyis depressed, current is switched in the opto-electronic arrangement from a normal current path to an alternate current path including the selected light source and its. latching photoconductive element to the secdary voltage supply. The result is that the common voltage level is depressed sufficiently so as not to support light source conduction in any of the other optoelectronic arrangements. However, the secondary voltagesupply is of sufficient magnitude along with the now depressed common operating voltage to maintain the selected opto-electronic arrangement in latched condition. When the key is returned, the optical switch reverts to a light resistance state to effectively disconnect the secondary voltage source and normalize the common operating voltage which now singularly maintains the selected optoelectronic arrangement in latched condition.

The cost of the terminal data set is reduced to a minimum by modular packaging of the light sourcesand also the photoconductive elements comprising each optoelectronic arrangement in fixed geometric arrangement. By employing such packaging techniques, the terminal data sets in accordance with this invention are assembled with greater ease and at lower cost than those heretofore possible. In addition, the problem of maintenance of these terminal data sets is substantially reduced in that a failure, once recognized, is swiftlyand effectively corrected on substitution of a packaged arrangement. A failure is easily recognized as only one latched optoelectronic arrangement in a particular field should provide a visual indication to the operator.

The foregoing and other objects, features, and ad vantages of the invention will be apparent from the following more particular description of preferred embodi- 3 ments of the invention, as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a partial schematic View of a single field of a terminal data set in accordance with this invention having no mechanical linkages or switches.

FIG. 2 is a schematic view of another embodiment this invention wherein mechanical switches are employed in lieu of the optical switches shown in FIG. 1.

FIG. 3 is a graph illustrating the voltage-current characteristics of a light source of the neon type which may be employed in the practice of this invention.

Referring to FIG. 1, each of numerous independent fields of the terminal data set includes a number of depressable keys 1 each having associated therewith an opto-electronic arrangement generally indicated at 3. It is to be understood that a terminal data set would include a number of independent field such as illustrated in FIG. 1; further, the arrangement of keys 1 and also the optoelectronic circuits and components comprising each of the opto-electronic arrangements 3 is for purposes of illustration only. Innumerable key arrangements to provide maximum operator efiiciency and also innumerable arrangements of the particular circuits and components to facilitate modulator packaging thereof will become apparent to those skilled in the art upon consideration of the description hereinafter set forth.

As illustrated in FIG. 1, each opto-electronic arrangement 3 comprises photoconductive elements 9 and 10 and "also a selected number of photoconductive elements 11,

12, 13, and 14 in fixed geometric arrangement so as to be illuminated by a light source or neon bulb 15 when fired. The photoconductive elements 9 through 14 are, for example, of cadmium sulfide (C(18) and exhibit a low resistance, e.g., in the order of 10 to 100 kilohms, in a light resistance state when illuminated by neon bulb 15; in a dark resistance state, the photoconductive elements exhibit a very high resistance, e.g. in order of several megohms. In each of the opto-electronic arrangements 3, the photoconductive element 9 is serially connected between a neon bulb 17 and a positive voltage source 19 along a current limiting resistor 21. The number of photoconductive elements 11 through 14 included in each opto-electronic arrangement 3 are connected in coded fashion between pairs of conductors 23, 24, 25, and 26, respectively, to form an encoder array. For example, the encoder array is formed by depositing the pairs of conductors 23 through 26 and photoconductive elements 11 through 14 in printed circuit fashion onto a substrate or card positionable within theterminal data set. Those photoconductive elements '11 through 14 included in each opto-electronic arrangement 3 and illuminated by neon bulb 15, respectively, when such encoder array is positioned are connected by dashed lines. The pairs of lines 23 through 26 are connected to input terminals of a transmitter 7; the output terminal of transmitter 7 is connected along a transmission line to a remotely-located central processing center 8.

The remaining photoconductive element is adapted to latch theopto-electronic arrangement 3 when neon bulb is'fired on depression of associated key 1. As shown, the photoconductive element 10 is serially arranged with neon bulb 15 to define a first current path in the optoelectronic arrangement 3; a second or normal current path is defined by a Voltage divider arrangement comprising resistors 27 and29 arranged in parallel with the photoconductive element It) and the neon bulb 15. The junction of the resistors 27 and 29 is directly connected to the junction of the photoconductive element 10 and neon bulb 15. .As hereinafter further described, biasing voltages for neon bulbs 15 are developed across the respective resistors 29.

A positive voltage source 31 is multipled to each of the opto-electronic arrangements 3 associated with a single field through a current limiting resistor 33 and along a common bus 35 at the junctions of the resistors 27 and the photoconductive elements 10. The voltage level along common bus is in excess of voltage V (see FIG. 3) necessary to sustain a neon bulb 15 operated. In addition, each opto-electronic arrangement 3 includes a negative voltage source 37 connected through current limiting resistor 39 to the junction of resistor 29 and neon bulb 15. The negative voltage source 37 and resistor 39 are paralleled by an optical switch 41 in the form of a photoconductive element. Eachoptical switch 41 is normally illuminated by a light source 43, i.e. close to clamp the junction of the neon bulb 15 and resistor 29 at substantially ground potential. When an opto-electronic arrangement 3 is unlatched, i.e. neon bulb 15 is extinguished, current flow is essentially from the common bus 35 and through the resistors 27 and 29 to ground through closed switch 41, the resultant voltage drop across resistor 29 being less than the firing or operating voltage of the neon bulb (see FIG. 3). When an opto-electronic arrangement 3 is in a latched condition, i.e. neon bulb 15 is fired and photoconductive element It is illumi nated, current fiow is essentially from the common bus 35 and through the illuminated photoconductive element 10 and the parallel arrangement of neon bulb 15 and resistor 29 to ground through closed optical switch 41. Total current flow along the last-defined path is relatively low so that the voltage level along the common bus 35 is almost equal to that of the positive voltage source 31 and the voltage across neon bulb 15 is in excess of the sustained operating voltage V (see FIG. 3).

As indicated from the description above, each of the optoelectronic arrangements 3 has three possible operating states: (1) a latched state wherein neon bulb 15 is fired to illuminate photoconductive elements 9 through 14 and switch 41 is closed, (2) an unlatched state wherein neon bulb 15 is extinguished and switch 41 is closed and (3) a transitional or latching state wherein eon bulb 15 is being fired and switch 41 is open. The transitional or latching state of an opto-electronic arrangement 3 is initiated upon switch 41 reverting to its dark resistance or open condition in response to the depression of the associated key 1. When key 1 is depressed, shutter element 45 supported by arm arrangement 47 travels downwardly to intercept light from source 43 incident on optical switch 41 to return the photoconductive element to its dark resistance state. It is to be noted that in the embodiment of FIG. 1 wherein optical switches 41 are employed, there are neither mechanical linkages nor move ment in the terminal data set other than the movement of key 1 and arm arrangement 47. When switch 41 reverts to its dark resistance or open condition, the junction of neon bulb 15 and resistor 29 is unclamped and the negative voltage source 37 is eifectively connected thereto.

The resultant voltage drop across resistor 29 due to the increased current flow exceeds the voltage V (see FIG. 3) and the parallelly-arranged neon bulb 15 fires to illuminate photoconductive element 10. When photoconductive element 1% reverts to a light resistance state, it is effective to latch the neon bulb 15. While key 1 is depressed and optical switch 41 is maintained in a dark resistance state, current flows from the common bus 35, the photoconductive element 19, and the parallel arrangement of resistor 29 and neon bulb 15 to negative voltage source 37 through current limiting resistor 39. Resistor 27 is now shunted by the light resistance of the photoconductive element 10. Due to the negative voltage source 37 and while the photoconductive element 19 is in a light resistance state, the voltage level along common bus 35 is depressed sufficiently so as to reduce the voltage at the junction of the illuminated photoconductive element 10 and neon bulb 15 of a previously latched one of the opto-electronic arrangements 3 below the sustaining potential V (see FIG. 3). Also, a corresponding reduction in voltage level is reflected at the junction of the resistors 27 and 29 of all remaining opto-electronic arrangements 3.

When the key 1 is released and elevated to normal position by action of spring 49, shutter 45 is carried upward and optical switch 41 is again illuminated by source 43. Switch 41 reverts to its light resistance condition to again clamp the junction of neon bulb 15 and resistor 29 to ground potential. Consequently, the voltage level along common bus 35 normalizes such that the voltage at the junction of photoconductive element and neon bulb exceeds the sustaining potential V and optoelectronic arrangement 3 is maintained latched. The voltages at the junctions of the resistors 27 and 29 in the remaining opto-electronic arrangements 3 increase slightly but do not exceed the firing potential V of neon bulbs 15. By selecting the ohmic value of resistor 27 in excess of the light resistance value of the photoconductive element 10, improper firing of a neon bulb 15 is positively avoided. An opto-electronic arrangement 3 continues in a latched conditionuntil such time that another key 1 is depressed to latch its corresponding opto-electronic arrangement, as hereinabove described.

The latching/interlocking aspects of applicants invention, therefore, are predicated upon the selective control of the resistance states of optical switches 41 whereby voltages developed across neon bubs 15, respectively, in opto-electronic arrangements 3 are either in excess of the firing voltage V greater than the sustained operating voltage V but less than the firing voltage V or less than the voltage V Further, due to the particular structure of applicants embodiment wherein each of the opto-electronic arrangements 3 in a field of the terminal data set are multiplied to a common bus 35, one and only one of such arrangements can be in a latched condition at any one time.

While an opto-electronic arrangement 3 is latched, the photoconductive elements 11 through 14 included therein are illuminated and complete electrical circuits between pairs of conductors 23 through 26, respectively, form the encoder array. In etfect, illumination of the particular photoconductive elements 11 through 14 generates a multibit signal indicative of the depression of the associated key 1. For'example, when the extreme right optoelectronic arrangement 3 is latched, each of the photoconductive elements 11 through 14 included therein is illuminated to complete electrical circuits between each er the pairs of lines 23 through 26 respectively. Accordingly, a multibit binary signal, e.g. 1111, is encoded and directed along the pairs of lines 23 through 26 to the transmitter 7. Conversely, the absence of a photoconductive element 11, 12, 13, or 14 is indicative, for example, of a binary 0. It is to be noted that multibit signals generated at the various fields of the terminal data set are applied continuously to appropriate input terminals of the transmitter 7 during such time that an optoelectronic arrangement 3 is latched. This allows for a complete message to be assembled for transmittal to the central processing center 8. When the completed message has been assembled, an End of Message switch 6 is closed by the operator to energize the transmitter 7. The transmitter 7 is operative, for example, to serially transmit the multibit signals applied at input terminals corresponding to each field of the terminal data set successively and in predetermined sequence along line 5 to central processing center 8 for processing in a manner well known in the art.

Further illumination of photoconductive element 9 while an opto-electronic arrangement 3 is latched results in increased voltage across light source 17 in excess of its firing potential V The light source 17 is selectively positioned in the terminal data set so as to provide a visual indicationthat the associated key 1 has beenpreviously depressed, in the illustrative embodiment, this indication isprovidedby a luminescent collar 51 which supports the stem of key 1 within an aperture provided in the terminal data set keyboard 53. l V

In FIG. 2, an alternate embodiment of this invention is schematically illustrated wherein mechanical switches 57 have been substituted for the optical switches 41 of FIG. 1. In this arrangement, similar numerical designations have been employed as in FIG. 1 to identify corresponding circuit elements. In the showing of FIG. 2, the photoconductor elements and 11 through 14 have been purposely omitted. As illustrated, operating voltages are supplied from voltage source 31 and through current limiting resistor 33 along the common bus 35 which is again multiplied to each of the opto-electronic arrangements 3. In each of the opto-electronic arrangements, the photoconductiveelement 10 is arranged in series with the parallel combination of resistor 29 and the neon bulb 15 to ground. While photoconductive element 10 is in a dark resistance state, current flow through the resistor 29 is insufiicient to bias neon bulb 15 in excess of its firing potential V A normally-open, mechanical switch 57, however, is connected across the photoconductive element 10 and is adapted to be closed upon a depression of an associated key of the terminal data set. For example, mechanical switch 57 is closed upon key depression by an arm arrangement similar to that shown in FIG. 1. When mechanical switch 57 is closed to bypass the high dark resistance of photoconductive element 19, the resultant voltage drop across resistor 29 is in excess of the firing potential V of the associated neon bulb 15. As in the embodiment of FIG. 1, the photoconductive element 10, when illuminated, is effective to latch neon bulb 15 so as to maintain the'opto-electronic arrangement 3 in a latched condition. When the neon. bulb 15 has fired and while the associated mechanical switch57 is closed in by-pass of the now illuminated photoconductive element 10, the voltage level along common bus 35 is depressed sufiiciently to extinguish a previously-fired neon bulb 15 in any of the remaining opto-electronic arrangements due to the voltage dividing action of the corresponding photoconductive element 10 and the parallel arrange-' ment of the neon bulb 15 and resistor 29. When mechanical switch 57 opens upon key release, the voltage level along common bus 35 normalizes to maintain the asso ciated opto-electronic arrangement 3 in a latched condition. In the present embodiment, therefore, the effective by-passing of the illuminated photoconductive element 10 by the mechanical switch 57 serves a similar function as did the negative voltage source 37 and optical switch 41 r of FIG. 1 in depressing the voltage level along common bus 35 sutficiently to insure the unlatching of any of the other optoelectronic arrangements 3.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. In a system, a plurality of latchable means, each of said latchable means being operative upon application thereto of a first predetermined voltage level and capable of sustained operation upon application thereto of a second predetermined voltage level, common biasing means multiplied to said latchable means and operative to apply a voltage at least equal to said second voltage level to each of said latchable means while one of said latchable means is operated, and additional means including secondary biasing means coactive with said common means for biasing another of said latchable means in excess of said first voltage level so as to operate and latch, said last-mentioned means including means operative to depress said voltage applied to each of said latchable means by said common means below said second predetermined voltage level whereby said one latchable means is disabled, said last-mentioned means being further operative to sustain said other latchable means whilesaid voltage applied by said common means is depressed.

2. In a system as defined in claim 1 wherein each of said latchable means includes a photoconductive element in tandem latching arrangement with a light source having a characteristic operating voltage and a characteristic sustained operating voltage.

3. In a system, a plurality of latchable means each having operating voltage and sustained operating voltage characteristics and each comprising a photoconductive element in tandem latching arrangement with a light source, means for normally applying a common bias in excess of said sustained operating voltage but less than said operating voltage to each of said latchable means, and additional means coactive with said common bias means for temporarily biasing another of'said latchable means in excess of said operating voltage, said common bias being depressed below said sustained operating voltage upon operation of said other latchable means, said additional means being cooperative with said common means to apply'at least said sustained operating voltage to said other latchable means while said common bias is depressed whereby the operations of said latchable means are mutually exclusive.

4. In a system, a plurality of latchable means, each of said latchable means being operative upon application thereto of a first predetermined voltage and capable of sustained operation upon application thereto of a second predetermined voltage, said latchable means being further' characterized in exhibiting a lower overall impedance while in an operated condition than in an unoperated condition, biasing means multiplied to one end of each of said latchable means for providing a common voltage to said latchable means in excess of said second predetermined voltage, means connected to the other end of each of said latchable means and coactive with said biasing means for selectively biasing an unoperated one of said latchable means in excess of said first predetermined voltage whereby said one latchable means is operated and exhibits said lower overall impedance, said selective biasing means being of sufficient magnitude to depress said common voltage below said second predetermined voltage while biasing said one latchable means in excess of said second predetermined voltage.

5. In a system, a plurality of opto-electronic arrangements each comprising a photoconductive element in tandem latching arrangement with a light source having a characteristic operating voltage and a characteristic sustained operating voltage, means multiplied to said photoconductive elements for applying a common bias to each of said arrangements, said common bias being of sufficient magnitude to normally sustain a light source while its associated photoconductive element is in a light resistance state but of insufficient magnitude to operate a light source while its associated photoconductive element is in a dark resistance state, means for selectively biasing one of said light sources in excess of said operating voltage to illuminate its associated photoconductive element whereby the corresponding one of said arrangements is operated to latch, a latching of said one arrangement being effective during the operation of said selective biasing means to depress said common bias sufiiciently so as not to sustain a light source in another of said arrangements and while its associated photoconductive element is in a light resistance state whereby only one of said arrangements is in a latched condition at any one time.

6. In a system as defined in claim wherein said common bias so applied is in excess of said characteristic operating voltage and wherein said selective biasing means includes impedance means in parallel arrangement with said light source and switching means in by-pass arrangement with its associated photoconductive element.

j 7. In a system as defined in claim 5 wherein said selective biasing means includes a first and a second impedance means in parallel arrangement with said light source and its associated photoconductive element, respectively, a voltage source connected to the junction of said light source and said second impedance means, and

clamping means connected to said junction in by-pass of said voltage source.

8. In a system as defined in claim 7 wherein the magnitude of said first impedance means-is greater than the impedance of said associated photoconductive element in a light resistance state.

9. In a system, a plurality of opto-electronic arrangements each comprising a light source having a characteristic operating voltage and a characteristic sustained operating voltage in tandem latching arrangement with photoconductive means positioned to be illuminated thereby, said arrangements also comprising a first and-second impedance means in parallel arrangement with said light source and said photoconductive means, respectively, common voltage means and a plurality of individual voltage means, each of said plurality of arrangements being connected between said common voltage means and one of said individual voltage means, the relative magnitudes of said common voltage means and said individual voltage means being sufiicient to develop voltage at least in excess of said characteristic operating voltage across said first impedance means so as to operate said parallellyarranged light source to illuminate its latching photoconductive means and means for clamping said individual means to a level intermediate said relative magnitudes whereat voltagesat least in excess of said characteristic sustained operating voltages are developed across an operated light source while its latching photoconductive means is illuminated and means for selectively inhibiting said clamping means.

10. In a system as defined in claim 9 wherein said clamping means comprises photoconductive elements in shunt relationship one with each of said individual means and means for normally illuminating said photoconductive elements.

11. In a system as defined in claim 9 wherein the magnitude of each of said individual means is sufficient upon a latching of said connected arrangement to depress said common means to a level whereat said characteristic sus rained operating voltage is not maintained across an operated light source in a previously latched one of said arrangements while its latching photoconductive element is illuminated and said individual means connected to'said previously latched arrangement is clamped to said intermediate level and wherein said depressed common means and said individual means are coactive to maintain said characteristic sustained operating voltage across said light source in said connected arrangement while its latching photoconductive element is illuminated.

12. In a system, a first and a second latchable means, each of said latchable means comprising a light emitting source operative upon application thereacross of a first.

predetermined voltage and capable of sustained operation upon application thereacross of a second predetermined voltage in tandem latching arrangement with a photoconductive element adapted to be illuminated thereby, common voltage means multipled to each of said photoconductive elements, said common voltage means having a magnitude in excess of said first predetermined voltage and at least sufficient to develop said second predetermined voltage across a light source while its associated photoconductive element is in a light resistance state,

means for selectively connecting said common voltage means to particular ones of said light sources in by-pass of corresponding ones of said photoconductive elements,

the magnitude of said common voltage means'being furcurrent path in parallel arrangement therewith comprising a photoconductive element in tandem latching arrangement with a light source, the junctions of said resistor elements and said light source and photoconductive elements, respectively, being electrically connected, the impedance of said second current path being greater than that of said first current path when said light source is unoperated and said photoconductive element is in a dark resistance state and less than that of said first current path when said light source is operated and said photoconductive element is in a light resistance state, said latchable means being multipled at one end to a first potential means and individually connected at the other end to a second potential means, the relative magnitudes of said first and second potential means being sufficient to sustain a light source while its photoconductive element is in a light resistance state, and means for varying current fioW along said first current path in a selected one of said latchable means to operate said included light 1% source, the operation of said included light source and subsequent illumination of said latching photoconductive element resulting in a switching of current along said sec ond current path to depress said first potential means below that level necessary to sustain a light source in the other of said latchable means.

References Cited by the Examiner Standeven: Opto-Electronic Ring Counter, IBM Technical Disclosure Bulletin, vol 2, N0. 2, August 1959, pp. 64 and 65.

Sponsler: Electroluminescent Trigger Circuit, IBM Technical Disclosure Bulletin, vol. 3, No. 4, September 1960.

Lynott: Photo Keyboard, IBM Technical Disclosure Bulletin, vol. 3, No. 11, April 1961.

RALPH G. NILSON, Primary Examiner, 

1. IN A SYSTEM, A PLURALITY OF LATCHABLE MEANS, EACH OF SAID LATCHABLE MEANS BEING OPERATIVE UPON APPLICATION THERETO OF A FIRST PREDETERMINED VOLTAGE LEVEL AND CAPABLE OF SUSTAINED OPERATION UPON APPLICATION THERETO OF A SECMULTIPLIED TO SAID LACTHABLE MEANS AND OPERATIVE TO APPLY MULTIPLIED TO SAID LATCHABLE MEANS AND OPERATIVE TO APPLY A VOLTAGE AT LEAST EQUAL TO SAID SECOND VOLTAGE LEVEL TO EACH OF SAID LATCHABLE MEANS WHILE ONE OF SAID LATCHABLE MEANS IS OPERATED, AND ADDITIONAL MEANS INCLUDING SECONDARY BIASING MEANS COACTIVE WITH SAID COMMON MEANS FOR BIASING ANOTHER OF SAID LATCHABLE MEANS IN EXCESS OF SAID FIRST VOLTAGE LEVEL SO AS TO OPERATE AND LATCH, SAID LAST-MENTIONED MEANS INCLUDING MENS OPERATIVE TO DEPRESS SAID VOLTAGE APPLIED TO EACH OF SAID LATCHABLE MEANS 